1) Field of the Invention
The present invention relates to a type of seal used in a rotatable valve. A valve member, pivotally disposed in a valve housing, makes contact with the seal to form a leak-tight boundary in the valve housing to secure a flow of fluid through the valve. Specifically, the invention relates to an improvement in the seals used in these valves.
2) Description of the Related Art
Valves having resilient seals are widely used in commerce and have a multitude of applications. Such valves are commonly used in fluid piping systems to stop and start the flow of fluid through the piping system. The specific construction of these valves differs widely depending upon the application in which the valves are used. Generally, the valves of the type to which the present invention pertains include a valve housing with an inlet and outlet port, a hollow interior defining a volume through which fluid flows between the inlet and outlet ports, and a rotatable valve member mounted within the interior of the valve housing. The valve member is pivotably disposed within the hollow interior of the valve housing about an axis which is generally perpendicular to the flow of fluid through the valve. Generally, the valve member is mounted on a shaft that extends through the hollow interior of the valve housing. The shaft is turned by a mechanical drive system for opening and closing the valve. When the valve member is rotated to a position that defines a plane which is generally parallel with the direction of fluid flow, the valve is fully open. When the valve member is rotated to a position that defines a plane which is generally perpendicular to the direction of fluid flow, the valve is closed.
To provide a leak tight boundary within the valve housing, the valve is provided with a seal. In conventional construction of these valves, the seal has many forms. Generally, the seal is an annular member positioned in the interior of the valve body that is adapted to contact the valve member as the valve member rotates to the closed position. Often the seal is affixed to the interior of the valve housing by means of an interior annular groove in the valve housing. The groove helps retain the seal in a position where it will contact the perimeter of the valve member when the valve member is in the closed position to form a leak tight boundary between the valve and the valve housing under a wide range of pressures and fluid flow conditions. Conventional valve construction also involves the use of mechanical means such as adhesives, frictional engagement, welding, and riveting to help retain the seal in position in the annular groove of the valve housing interior.
In some prior art valve structures, such as the one disclosed in U.S. Pat. No. 3,544,066, a curable polymeric material, such as epoxy resin is used to retain the valve seal within the internal annular groove of the valve body. In the ""066 patent, the seal is constructed from a Buna-N type of rubber material with 60-75 durometer hardness. The valve seal is inserted into the internal annular groove and the epoxy resin is introduced, in liquid form, between the annular exterior surface of the seal and the internal annular groove. The integrity of the seal formed in this manner is dependent upon the epoxy""s bonding strength and the amount of epoxy coverage between the seal and groove surfaces. Thus, as disclosed in the ""066 patent and in later designs of seals for use in conventional valves, the surface area of the seal and groove surfaces exposed to the epoxy is increased to raise the relative strength of the bond between the seal and the groove. In the ""066 patent, the seal is formed with a grooved inner surface to increase the seal inner surface exposed to the epoxy, and thereby improve the gripping co-action between the seal and the epoxy resin to bond the seal to the groove.
To assist in retaining the seal within the interior annular groove of the valve housing, conventional valve designs use a seal with a formed profile that interlocks with the formed groove profile in the housing of the valve. In U.S. Pat. No. 3,799,501 such a structure is disclosed. In the ""501 patent, the seal is formed with annular fins on its side faces that cooperate with the chevron cross section of the annular groove formed in the interior surface of the valve housing. To provide the maximum amount of frictional engagement between the seal and the groove, the profiles are closely matched. When the valve member is moved to the closed position, the elastomer ring compresses under the force of the valve member and interlocks tightly with the annular groove.
However, the use of both of these techniques to secure the seal in the valve housing has been a continuing challenge to designers of these valves. Epoxy resin alone has been found to be insufficient to retain a seal in the groove under extreme flow conditions. For example, under a throttle flow condition, wherein an extreme pressure differential exists between the upstream and downstream sides of the valve (e.g., when a valve is only slightly open and fluid is forced through a highly restricted area), differential pressures acting on the valve seal may cause the relatively large volume of epoxy under the seal to deform, thus moving the seal in the annular groove. Without a structure surrounding the seal to retain the seal in position in the valve housing (an interlock), the seal may fail to seat against the valve member when the valve member is returned to the closed position. In this situation, the integrity of the leak tight boundary of the valve is breached.
On the other hand, when the profiles of the seal and the valve housing or groove are closely matched so as to provide a maximum amount of surrounding and gripping co-action between the two surfaces, the injected epoxy cannot be consistently and evenly dispersed between the two surfaces to effectively bond the surfaces together. As a result, the integrity of the seal may also be compromised, since a portion of the seal may be held in the groove only by the frictional cooperation of the inter-engaging profiles.
The use of a closely matched and tight fitting interlock between the seal and the interior annular groove has other draw backs. The cost of constructing a valve using a system of inter-engaging profiles increases with the complexity of the form of the interlock. Generally, the valve housing is cast with the annular groove having the formed profile for the interlock. In order to increase the frictional engagement and strength of the interlock, the formed profile used in the annular groove must be fabricated with a relatively high level of dimensional accuracy so that it closely matches the complementing formed profile on the seal. This high level of dimensional accuracy requires more stringent manufacturing controls for both the seal and the valve housing/groove, thus increasing the cost of the valve.
When a more closely matched formed profile and tighter fitting interlock is used between the seal and the groove to increase the frictional engagement, the seal becomes more difficult to install in the groove. Using conventional installation methods, the seal is mechanically forced into the groove. Although the seal is generally flexible and compressible, when the interlock between the seal and the groove is tightly controlled during manufacture, the amount of force needed to insert the seal in the groove dramatically increases because of the near interference fit between the seal and the groove. Consequently, during installation of the seal in the groove, the large amount of force exerted on the annular interior surface of the seal may result in damage to the seal as it is inserted into the groove. Since the interlock portion of the seal generally has the smallest cross section, the interlock surfaces of the seal may not be able to withstand the amount of force needed to install the seal in the groove. Hence, the damage may be sustained on the seal portion of the interlock, where the resultant damage decreases the ability of the interlock to frictionally hold the seal in the internal annular groove.
Thus, there is a need for a valve seal that effectively incorporates the advantages of both an interlock system and a epoxy resin to withstand high stress flow conditions without loosing the ability to maintain an effective seal. Further, under certain extremely high stress conditions, such as the throttle flow condition, there is a need for a valve seal that will resist failure. Still further, there is a need for a valve seal that does not require complex or cumbersome installation. Still further, there is a need for a valve seal that does not significantly increase the manufacturing costs associated with the valve.
Among the several advantages of the present invention over the prior art may be noted the provision of a valve seal that is capable of withstanding high stress flow conditions without loosing its ability to maintain an effective seal; the provision of a valve seal that is constructed to resist failure even in high stress flow conditions, such as a throttle flow condition; and the provision of a valve seal that does not require a complex or cumbersome installation; and a valve seal that does not significantly increase costs associated with manufacturing the valve.
In one aspect of the invention, a seal is installed in an internal annular groove in a valve housing for a rotatable valve. This seal is a resilient ring dimensioned to fit inside the internal annular groove when the ring is inserted into the internal annular groove. The ring has an annular interior surface, an annular exterior surface, and axially opposite first and second circular end surfaces that extend radially between the annular interior surface and the annular exterior surface. The ring has a cross-sectional area that leaves at least one void between the internal annular groove and the first and second circular end surfaces of the ring when the ring is inserted into the annular groove. These voids allow the epoxy injected into the internal annular groove to flow through the voids between the seal and the groove, thus holding the seal in the groove.
In yet another aspect of the invention, the seal includes the resilient ring affixed in the internal annular groove of the valve housing for the rotatable valve. The groove has a center axis, and a bottom wall and a pair of side walls extending around the center axis. The ring has an annular interior surface, an annular exterior surface that opposes the bottom wall of the internal annular groove, and axially opposite first and second circular end surfaces that oppose the side walls of the internal annular groove. The ring has a cross-sectional area that leaves voids between the side walls of the internal annular groove and the first and second end surfaces of the ring. In this arrangement epoxy can be deposited in the internal annular groove between the bottom wall of the groove and the annular exterior surface of the ring, and in at least some of the voids between the side walls of the groove and the first and second end surfaces of the ring.
To increase the strength of the bond between the seal and the groove, the surface area of the groove and the side walls is increased. Slots are formed in the side walls of the internal annular groove and lobes are formed in the seal that project from the first and second circular end surfaces of the ring. To provide an interlock, the lobes of the ring project into the slots formed in the side walls of the groove. The lobes have rounded ends that are received in the slots formed in the side walls of the groove and the lobes define voids between the rounded ends of the lobes and the slots. The slots also have rounded roots to allow the epoxy to firmly bond the seal in the groove wall and permit epoxy to more evenly disperse around the seal in the groove.